In the photo-stimulable phosphor imaging system, as described in U.S. Pat. No. Re. 31,847 reissued Mar. 12, 1985 to Luckey, a photo-stimulable phosphor sheet is exposed to an imagewise pattern of high energy short wavelength radiation, such as x-radiation, to record a latent image pattern in the photo-stimulable phosphor sheet. The latent image is read out by stimulating the phosphor with a relatively long wavelength stimulating radiation, such as red or infrared light. Upon stimulation, the photo-stimulable phosphor releases emitted radiation of an intermediate wavelength, such as blue or violet light, in proportion to the quantity of short wavelength radiation that was received. To produce a signal useful in electronic image processing, the photo-stimulable phosphor sheet is scanned in a raster pattern by a beam of light produced for example by a laser deflected by an oscillating or rotating scanning mirror, and the emitted radiation is sensed by a photodetector such as a photomultiplier tube, to produce the electronic image signal.
In more recent apparatus, the light emitted from the phosphor is collected by a wide aperture collector such as a mirror box or transparent collector, and sensed by a photomultiplier tube. Any persistent decay of the phosphor is detected by the wide aperture collector and degrades the signal produced by the apparatus.